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Old 04-06-2001, 09:27 AM   #1
Gage
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Question What are performance advantages of all wheel drive?

I live in Memphis Tennessee, USA. I have never owned an all wheel drive vehicle.
If a 2002 WRX was modified to produce about 250 to 260 horsepower, (I have read that such numbers are not unrealistic with an investment of 2 to 3 thousand dollars) how would it handle in quarter mile race against a 1999 to 2000 Ford Mustang producing 260-280 horsepower. (I’m not sure what the horsepower is on a factory V-8 non cobra Mustang)

I am familiar with All Wheel Drive, but what advantage does it provide in an acceleration from stop? Is the most valuable aspect of AWD in the Impreza…the fact that handling is so much better and safer in all weather conditions? I know that may seem like a dumb question. I’m learning as I go.


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Old 04-06-2001, 09:33 AM   #2
Hondaslayer
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GRIP while that rustang is spining his tires your on your way down the track
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Old 04-06-2001, 09:48 AM   #3
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Think of it another way:

1) Mustang @280hp thru 2 wheels.

2) Impreza @280hp thru 4 wheels.

The question becomes, at what horsepower to traction ratio will the tires break loose and spin. If the tires break loose at LESS than 280hp, the Mustang will NOT be able to put all the power to the ground. The Impreza will.

Yes the Mustang will probably get you approaching the top end of speed, but that's 'cause of the gearing. I believe they have a higher gear ratio and will top spped you out. But other than that, the Mustang will be toast.

Now try that again in the rain, sleet, snow, sand, mud, AWD will beat <u>just about</u> anything off the line in those conditions. The Mustang will sit and spin...

-Rez
<IMG SRC="http://www.reverberations.com/images/scrambles.gif" border=0>

[This message has been edited by Rez (edited April 06, 2001).]
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Old 04-06-2001, 09:56 AM   #4
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If you are competing again a Mustang or any other V8 cars on a 1/4 mile track, you'll lose.

If you add turns, mud, rain, etc etc on the track, AWD got more advantage in handling.

A good car needs power, braking, and handling. Mustang lacks handling.
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Old 04-06-2001, 10:02 AM   #5
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Just a question:

If you have two equally weighted cars. (i'm not saying that the mustang and the rex are).

And they have the same tires.

And the same HP.

On dry pavement.

Why would the AWD car start faster? According to physics the traction should be the coeficient (can't spell, sorry) of friction times the normal force, both of which should be the same on both cars. The surface area shouldn't make any difference.

I could see how the AWD would help you on slick conditions, as you have more of a chance (4wheels vs 2), of contacting a patch of ground with a high coeficient of friction (and of course the ability of the power to be routed between front and back, and side to side in the back). But I just don't see how AWD would help you on dry pavement.

Please Explain.
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Old 04-06-2001, 10:12 AM   #6
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You guys are smoking crack if you think AWD will help you in a 1/4 mile against a RWD car.

Under hard acceleration, most of the car weight is transferred to the back, which is why FWD cars usually don't have very fast sprint times. The AWD car is still sending power some to the front, which is essentially just power loss, while the RWD car is sending all the power to the rear, which has all the weight.

Assuming equal HP, and equal driver skill, a AWD will never beat a RWD, in any race, unless the road is slippery.
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Old 04-06-2001, 10:21 AM   #7
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the infamous AWD launch man. rev it up to 4000rpms slip the clutch, all four wheels grip and you take off like a bat out of hell, while the mustang is still trying to get traction.
there are few things on the road that can beat an AWD drive car off the line. however if your stock the mustang will catch up and pass you. the new mustangs have 260hp and 302 lb-fts of torque and weigh 3,250 lbs (WRX weighs 3085lbs) and are capable of running a 14 flat in the quarter mile while we are more like a 14.3-14.6 second car. however the cars have about the same 0 to 60 (mid to high 5's). a WRX w/ 250+hp would be able to take a stock new mustang GT down with out to much trouble id imagine.
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Old 04-06-2001, 10:24 AM   #8
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someone still needs to explain to me how you get more traction simply by having more surface area (ie. 4 wheels over 2).
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Old 04-06-2001, 10:38 AM   #9
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traction = friction

friction = surface to surface rubbing

more tires to the ground = more surface to surface rubbing

[This message has been edited by wcbjr (edited April 06, 2001).]
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Old 04-06-2001, 10:45 AM   #10
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In addition, you have to agree with me that tires DO have a power limit in which they break free and start spinning. Lets call that amount of power sent to that 1 tire "X". Now send that same power "X" to 2 tires, they won't spin because each tire is getting only 1/2 of the power "X".

Now for the 2 to 4 tire comparison. 2 wheel vehicles can handle 2*"X" amount of power. 4 wheel vehicles can handle 4*"X" amount of power because there are 2 more tires to send the power to. See?

This is assuming equal weight distribution to all 4 wheels. The comment of sending more weight to the back of RWD cars on launch throws the comparison off a bit, but not too much.

[This message has been edited by wcbjr (edited April 06, 2001).]
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Old 04-06-2001, 10:49 AM   #11
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>>>If you are competing again a Mustang or any other V8 cars on a 1/4 mile track, you'll lose.

Now that's just a stupid statement. He said he'd modify it to go 250-260 hp. That will beat a Mustang GT pretty easily on the 1/4 mile. You shouldn't make blanket statements like that. I can give you a list of V8-powered cars all freakin' day that are slower than a Kia Sephia. This isn't 1964 where the only thing that matters is displacement.
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Old 04-06-2001, 10:51 AM   #12
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>>>According to physics the traction should be the coeficient (can't spell, sorry) of friction times the normal force, both of which should be the same on both cars. The surface area shouldn't make any difference.

Because the amount of friction is determined by the surface area. There's a lot more friction when you're sending power to 4 wheels as opposed to 2.
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Old 04-06-2001, 10:51 AM   #13
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Quote:
someone still needs to explain to me how you get more traction simply by having more surface area (ie. 4 wheels over 2).
You have to remember that the friction coefficient will essentially become zero if you apply too much force over a period of time to that contact patch. So, let's say that our 250 RWD car is driving 200-210 RWHP @ 4000 RPM. That much power over time may overcome the friction coefficient. However, a similar 250 AWD car with a max 30-70 torque split may generate 140 RWHP and 60 FWHP at the same RPM. Now, the rear wheels have less power driven to overcome that friction force since part of it is driven up front, which has the added benefit of pulling the car along.

Of course, this doesn't talk about weight transfer, gearing, heat of tires etc since all these little things add up to the big picture but what I've outlined pretty much explains things in my point of view.

Ray
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Old 04-06-2001, 10:52 AM   #14
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Well....I'll speak from my experience with AWD. This is real world experience and not from a closed track or 1/4 strip.

Ever had to make a left turn into a highway froma dead stop before? Don't you hate it when your front wheel drive or rear wheel drive car spins its tires as you make the turn while accelerating? Feels like your going no where fast, doesn't it? Can you imagine if it was raining? I had that problem with my FWD Nissan Sentra. I thought if I would die in an accident, it would be in that situation. Ya gotta cross the first lane which has cars coming from your left, then you gotta worry about the car coming up on your rear once you get across!

I don't have that problem with my Impreza. When I hit the gas, the tires grab hold and GO! I can cross the first lane without a spin and once the car is on the other side, hit 2nd gear and the car just MOVES! No tire spinning there either.

That's the beauty of All Wheel Drive.

With the two wheel drive cars I've seen, they slipped when they first moved, they splipped again when they straightened out.



[This message has been edited by Snoopy (edited April 06, 2001).]
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Old 04-06-2001, 10:56 AM   #15
Aquavir
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Except you are forgeting your basic physics. Surface area has absolutely nothing to do with friction, unless it is somehow changing the coeficiant of friction...

Just figured it out...

The 2wd car doesn't get all the weight on the drive wheels, but the AWD does. In my scenario I was thinking of the weight of the car being distributed on the drive wheels. But in the 2WD car, the drive wheels only get half (if not less) of the weight (the non drive wheels have half the normal force which the ground is exerting on the car, so therefore that half is wasted). So therefore each drive wheel on both cars (AWD and 2WD) get the same amount of normal force, and therefore friction (not taking into account the whole thing about weight shifting back...i'm only a dental student...I don't want this getting too complex) and so the AWD car can put more power to the road.

Thanks for helping me work that out.

[This message has been edited by Aquavir (edited April 06, 2001).]
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Old 04-06-2001, 10:56 AM   #16
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>>>Assuming equal HP, and equal driver skill, a AWD will never beat a RWD, in any race, unless the road is slippery.

I'll give you the benefit of the doubt and assume that you're just young, instead of treating you like a moron.

What happens when you dump the clutch on a new corvette on dry pavement? It spins? For how long? Dump the clutch on an EVO II on the same pavement. What happens? It spins for 1 second. And takes off. Like a freakin' rocket. The EVO will have a 20 foot lead just in the first 100 ft of the race because of it.
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Old 04-06-2001, 11:01 AM   #17
Aquavir
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"Because the amount of friction is determined by the surface area"

Surface area does not determine friction.

[This message has been edited by Aquavir (edited April 06, 2001).]

[This message has been edited by Aquavir (edited April 06, 2001).]
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Old 04-06-2001, 11:05 AM   #18
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>>>Surface area has absolutely nothing to do with friction,

What Physics class did you learn that in?? That's not true at all. Friction has everything to do with surface area. That's why wider tires grip better. Ever notice how fat racing or drag tires are? The wider the tire, the more surface area there is with the tire's contact patch on the road. The more surface area, the more friction. The more friction, the less slip and more go.

[This message has been edited by bryanw (edited April 06, 2001).]
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Old 04-06-2001, 11:07 AM   #19
Aquavir
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I'm sorry but you're wrong. Friction is determined by the C of Friction X the normal force. Look it up.
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Old 04-06-2001, 11:13 AM   #20
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Rhung,

So would the reason wider tires grip better be because they disperse the power over a wider area; therefore making it less likely that the wheel will over come the CF?

Wouldn't the normal force at each point of contact decrease though, with increased SA, therefore making the friction at each point less as well?

Why do bigger tires give better traction?
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Old 04-06-2001, 11:15 AM   #21
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Quote:
Surface area has absolutely nothing to do with friction, unless it is somehow changing the coeficiant of friction...
What is friction? What is the coefficient of friction?

Friction is the ratio of normal force to surface area multiplied by the coefficient of friction.

Coefficient of friction will only change if the materials in contact alter their molecular states, i.e. are not the same materials. The amount of friction across the SAME surfaces can ONLY change due to normal force changes.

Say water gets in the way of the tire and street. The tire has a coefficient of friction with the water, very low I might add. The street has a coeffcient of friction with the water, very low too. End result - hydroplaning. The coefficient of friction changed because the materials changed.
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Old 04-06-2001, 11:18 AM   #22
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I like my answer better.

Less headache.
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Old 04-06-2001, 11:19 AM   #23
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that's what i'm trying to say with obviously less understanding, and not as eloquently.

if that's true, why do dragsters have such big a** tires?

[This message has been edited by Aquavir (edited April 06, 2001).]
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Old 04-06-2001, 11:21 AM   #24
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This is hopeless. This is common sense. I don't know what you're trying to accomplish, but you need to pull your head out of your ass. Anybody who doesn't understand that increased surface area increases friction is a ****ing moron. Sorry to be so rude, but you leave me no choice. Do you really want me to give you a jillion examples of this? Is it really that ****ing difficult to understand? Give me a single damn example of friction being exactly the same when surface area changes.
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Old 04-06-2001, 11:23 AM   #25
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I am by no means an expert on this, but I do know that many factors would come into play when comparing equal horsepower cars with different drivetrains. The gearing, weight, length of the race, type of race, and conditions of the road surface would all be determining factors in who would win in equal horsepower cars with these two different drivetrains. I would tend to think that a rear wheel drive car would usually win in a 1/4 mile drag race. This would be why the quickest 1/4 mile cars are RWD.
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